In Variable Definitions is said :
The month of the year the user signed up. Months are in chronological order but January is not necessarily month 1.
Do you have any idea how to edit it? For example, what could be the 1st month? (Febrauary, March or may ...)
Looks like 2 is July, 3 is August (they have 31 days)
{8:'January',9:'February',10:'March',11:'April',12:'May',1:'June', 2:'July',3:'August',4:'September', 5:'October', 6:'November', 7:'December'}